A computer macrosimulation system is being developed to provide, among other things, a methodology for estimating the number of acceptors of family planning required to attain population policy goals expressed in terms of period statistics. Particular attention is being given to the problem of estimating, by various demographic characteristics, the number of acceptors of IUD's, pills, other methods of contraception, abortion, and sterilization in successive cohorts that are sufficient to attain a policy goal, given some initial state of the population. A central part of the research in developing this methodology consists of constructing models of reproductive regimens, describing patterns actually followed by couples in the utilization of contraception, abortion, and sterilization to space and limit births. Taiwanese as well as other data with contraceptive-pregnancy histories coded in time series are being used to construct these model reproductive regimens. Research in statistical methods of estimation are also being undertaken whenever problems in data analysis are not covered by standard methods. BIBLIOGRAPHIC REFERENCES: Mode, C.J. (1976): Age-Dependent Branching Processes and Sampling Frameworks for Mortality and Marital Variables in Nonstable Populations. Mathematical Biosciences, in press. Mode, C.J. (1976): On the Calculation of the Probability of Current Family Planning Status in a Cohort of Women. Mathematical Biosciences, in press.